Consider extracting sendwal from Klio into a standalone Go module

[joao00001]

Hi all 😄. I've been reading through Klio's core/internal/client/sendwal package (the WAL streaming receiver: IDENTIFY_SYSTEM, replication slots, START_REPLICATION, timeline handling, built on pgx + pglogrepl). It's already written with a clean sink interface (buffer.Handler) that isn't Klio-specific, and it's one of very few working, tested implementations of Postgres WAL streaming in Go.

I think it's worth considering as a standalone module rather than something buried in Klio's internal/ tree, for a few reasons:

• cloudnative-pg/plugin-barman-cloud currently shells out to pg_receivewal/barman-cloud-wal-archive, so a native Go receiver would let it drop that dependency on external binaries.
• Any future CNPG-I backup plugin needs this same piece and shouldn't have to either vendor it from Klio's internals or reimplement it.
• Full disclosure: I'm on the Barman side at EDB, and we'd also like to use this in a Go-based Barman component down the line. Wanted to say that plainly rather than present this as purely altruistic. I think the module stands on its own merits for the reasons above, but you should know the interest exists.

Two things would need to happen for it to actually be extractable cleanly: right now receiver.go pulls in the full cloudnative-pg/cloudnative-pg operator module just for one function (SegmentFromName), and it talks to Klio's gRPC client directly instead of through the Handler interface it already has for the write side. Neither is a big lift, but they're real before/after conditions for this to be a genuinely lightweight library.

Not proposing pulling WAL filename/LSN parsing into this, since that already lives in machinery and should probably stay there. Curious whether this seems worth an issue + small prototype PR, and who from Klio's maintainers would want to be involved early given it touches module boundaries.

[gbartolini]

Thanks @joao00001. Sounds like a great idea to me, but I leave it up to @fcanovai, who's currently leading the Klio project, to respond.